How many watts per gallon with metal halide lighting

You must take into account the efficiency of the flourescent technology.
T12, T10, T8, T5 are all increasing in efficiency. T12 is the old stuff
with lowest efficiency. The watt/gal ratings were developed a long time ago
during that period. A PowerCompact is T5 and worlds apart from an old T12
bulb watt for watt. Wattage alone does not determine how much light is
produced. You must define the effciency. You need to consider lumens per
gallon not wattage per gallon.

I have a 100G tank and use 2 - 55W 24" 6700K PowerCompacts. That's 1W/G of
T5 technology. More than enough light. I have O2 bubbles coming off my
plants. Would not want more light, unless I was trying to raise plants for
sale needing ultra fast growth.

Chris.